NBC metereologist John Morales reacts to the scale of Hurricane Milton on the air. Photo: Screenshot / NBC
A respected hurricane forecaster went viral this week for choking up while warning Americans about the approaching Hurricane Milton.
Apologising for showing emotion on live TV, NBC meteorologist John Morales called Milton an "incredible, incredible, incredible hurricane" and warned those in its path in Tampa, Florida and the coast of Mexico's Yucatan Peninsula to get out while they could.
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What he said next was: "You know what's driving this, I don't need to tell you. Global warming, climate change."
"I mean, the seas, are just so, incredibly, incredibly hot."
The veteran broadcaster later explained on X that extreme weather driven by global warming had changed how he communicates as a meteoreologist.
"Frankly, YOU should be shaken too."
Tampa prepares for the arrival of Hurricane Milton on 9 October, 2024 in Tampa, Florida. Photo: SPENCER PLATT / GETTY IMAGES NORTH AMERICA / Getty Images via AFP
What's driving Milton?
The physical reason why stronger hurricanes can be linked to greenhouse gases is straightforward, even though the systems themselves are volatile.
Heat trapped by greenhouse gases warms the surface of the ocean, allowing storms forming over the ocean to gather more energy. Hotter air also holds more moisture, meaning more rain available to dump on storm victims.
Auckland University climate scientist Kevin Trenberth described in a blog post this week how 20 years ago, he struggled to convince hurricane forecasters that a string of hurricanes that made landfall in Florida in 2004 were worsened by global warming.
Kevin Trenberth. Photo: Chris Loufte
Trenberth is a top atmospheric scientist who spent much of his career working at the US National Center for Atmospheric Research.
He wrote that in 2004 it made sense to him that hotter seas would be supercharging hurricanes, but there was pushback from others in his field.
Now, the consensus view of scientists is that greenhouse gases have led to heavier rain in tropical cyclones.
Higher top wind speeds are also expected because of storms picking up more energy from hotter oceans.
As the world keeps heating, more hurricanes are expected to reach categories four and five.
As Trenberth summarised it in his blog: "While hurricanes occur naturally, human-caused climate change is supercharging them and exacerbating the risk of major damage."
Flooding seen in Dunedin recently. Photo: RNZ / Tess Brunton
New Zealand storms
New Zealand gets ex-tropical cyclones from the Pacific, meaning they have lost some of their energy since being a full-blown tropical cyclone - but they can still be severe.
Last year's Cyclone Gabrielle was one of those - one of the worst natural disasters New Zealand has experienced.
NIWA climate scientist Dáithí Stone and a group of other researchers published a study last month simulating what Gabrielle would have looked like, without global heating.
The planet has already heated just over 1C from fossil fuels and agricultural gases, which they found led the storm to dump about 10 percent more rain in total - and 20 percent more an hour, during the storm's peak.
If the planet heats another 1C, another 10 percent more rain is expected during storms like Gabrielle, but with a 30 percent increase in heaviness during the peak hours. (Global projections suggest another 1C is likely, even if countries meet their greenhouse gas targets - and it could be much more.)
Climate scientist Luke Harrington, of Waikato University, said no studies have yet looked at the effect global heating had on last week's Dunedin's floods.
But he said the combination of previous studies on Gabrielle and South Island weather events points to a likely increase in rain, compared to a world without climate change.
NIWA principal climate scientist Sam Dean said, based on previous studies, Dunedin likely received around 10 percent more rain than it would have without greenhouse gases.
"The frequency of such events in Dunedin may also be changing, however this question is more specific to a location as it depends on where and how fast storms are tracking past the country, so dedicated studies are usually required to give a reliable answer."
Coupled with heavier rain is sea level rise.
Low-lying parts of South Dunedin are at extra risk of floods, because sea level rise is pushing up the level of groundwater, leaving less dry ground able to absorb heavy rain.
According to Stats NZ the sea around Dunedin has risen about 18cm since 1901, and the pace it is rising at has doubled.